It is common practice to mount headrails for various window coverings using a spring clip device having an intermediate portion adapted to overlie the headrail and front and rear leg portions that extend downwardly from the intermediate portion for supportably engaging a head rail. In ceiling mount installations, the intermediate portion of the clip device is fastened by a screw or the like directly to the overhead support. In wall mount installations, the intermediate portion of the clip device is fastened by a screw, bolt or rivet either directly to the horizontal leg of a wall bracket or to a slidable extension of the wall bracket, for example as shown in U.S. Pat. No. 4,363,459. In order to adjust the spacing of the headrail from the wall or other vertical mounting surfaces, it is generally necessary to remove or at least loosen the fastener that attaches the clip to the wall bracket to enable adjustment of the clip relative to the upright support surface. However, the fastener that attaches the spring clip to the wall bracket is not readily accessible when the headrail is installed on the spring clip.